Booster and method of use



Jan. 27,1970 R, a CLAY ET AL 3,491,688

BOOSTER AND METHOD OF USE Filed May 1, 1968 ROBERT B. (LAY 00mm. 77 BAILEY United States Patent 3,491,688 BOOSTER AND METHOD OF USE Robert B. Clay and Donald T. Bailey, Bountiful, Utah, assignors to Intermountain Research and Engineering Company, Inc., a corporation of Utah Filed May 1, 1968, Ser. No. 726,278 Int. Cl. F42]: 1/02 US. Cl. 10224 4 Claims ABSTRACT or THE DISCLOSURE A small booster for detonating insensitive explosive charges is cast in wedge shaped configuration, at least roughly approximating a spherical segment, with a capreceiving recess formed along its wedge or thin edge portion. This recess is designed to place the effective center of the detonator at a position essentially opposite the center of mass of the booster so as to take maximum advantage of a spherical detonation wave or head which can thus be produced. By orienting the thus pri mered booster to take advantage of its maximum directional effect, full detonation of highly insensitive main charges such as aqueous AN-particulate fuel charges, AN -F0 charges, and the like, may be assured.

BACKGROUND AND PRIOR ART It has long been known that the orientation and mass arrrangement of material in a booster, or in any explosive charge, has a pronounced effect on the character of the explosion produced. In The Science of High Explosives. Reinhold Publishing Co., New York, 1958 (A.C.S. Monograph Series No. 139), pp. 91-122, especially pp. 105 and 121, Dr. M. A. Cook describes this phenomenon in detail. So far as applicants are aware, however, the art has: not effectively utilized the principles therein described.

For detonating highly insensitive blasting charges, such as charges of aqueous ammonium nitrate, particulate fuel, or of prills and oil, i.e., ammonium nitrate sensitized with fuel oil (ANFO) and the like, several procedures have been followed. In some of them, fairly large cap-sensitive masses of high explosive, such as PETN, Tetryl, Pentolite, etc., have been used. The amounts of booster materials required in such cases are considerable and the ingredients are relatively expensive. These methods have several faults, including hazards involved in handling and storing relatively large quantities of these easily detonable materials, the cost of the the materials, and detonation failures which may result from their improper placement within the charge to be detonated.

Multiple stage boosters such as those described in US. Patents Nos. 3,037,452, 3,037,453 and 3,371,606 have solved some of the problems mentioned above, reducing very substantially the total quantity of booster explosive required to detonate an insensitive main charge. These multi-stage boosters, however, are somewhat expensive tomanufacture because they require incorporation of a more sensitive (i.e., cap-sensitive) first stage or small sensitive charge, within a larger and less sensitive outer dharge. For use in many situations such boosters, designed as they are to protect the relatively sensitive inner core by means of a less sensitive outer sheath, are very satisfactory. In appropriate sizes they are useful for detonating very insensitive main charges, provided such main charges are of fairly large diameter or cross-section. These protected core boosters are commonly used, in sizes up to three or four inches in diameter, for detonating slurry blasting agents, etc., in large deep boreholes ice which may have diameters as great as ten to twelve inches or more.

For detonation of relatively insensitive explosives in small boreholes or in slender columns, the larger boosters described above cannot be used. In some cases they are too large to go in the borehole. In others their cost may be prohibitive, as in small shots, for example. There is need for a small but dependable booster which is low in cost but still effective to detonate explosive charges of low detonation sensitivity. One object of this invention is to provide such.

It is also desirable to retain control of all detonation devices, including boosters, even after they have been positioned in the charges, so that they can be removed from the charges prior to detonation, where necessary. Changes in plans or interruptions of blasting work due to weather or other causes, frequently make it desirable or necessary to pull out the booster. It may become necessary to do excavation work nearby which the presence of a booster might render very hazardous. It is common practice to attach caps and boosters in one way or another to the electric wire or to the priming cord or fuse used to set off the charge. If secured adequately, the primer or booster may be withdrawn by pulling on the wire or other connecting line. But with small boosters of prior art types, it has not been very convenient in many cases to secure them to the initiating line, with assurance that they can be pulled out of the charge if this becomes desirable. To accomplish this is another object of the invention.

A further object is to obtain maximum or near maximum boostering effect from small booster charges by improved design, thus improving economy and efiiciency. This is achieved by shaping the booster body to conform approximately to a spherical segment detonated at its spherical segment detonated at its spherical center.

SUMMARY In summary, a small generally wedge-shaped mass of cap-sensitive explosive approximating a small spherical segment in shape, is cast or otherwise formed so as to accommodate a conventional primer along its thinner edge portion. The detonator or initiator may be an ordinary electric blasting cap, or a length of detonable fuse of known type, or a fuse-initiated cap. The approximately wedge-shaped booster body member is arranged to have the effective detonating center of the cap, etc., positioned as nearly as convenient at its spherical center, i.e., directly opposite its center of mass, the mass being designed to take the fullest practical advantage of the spherical wave front or the generally conical configuration of the advancing detonation wave. It should be made as certain as possible also that the desired relationship between the cap and the booster will be maintained. For this purpose, the cap, or detonating fuse, etc., and the booster are securely fastened together by simply wrapping multiple convolutions of a thin strongly adhesive tape around them, and then manually crimping the tape tightly around both members to engage them more effectively. Tests show that strong pulls may be made, e.g., on the electric cord or other line connected to the booster, i.e., pulls strong enough to pull it out of several feet of aqueous slurry, for example, Without separating the caps from the booster or losing the latter in the main explosive mass.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective View of a booster per se of the present invention.

FIG. 2 is a front end view of the booster of FIG. 1.

FIG. 3 is a longitudinal cross-section of a simple mold suitable for forming the booster of FIGS. 1 and 2.

FIG. 4 is a front side view of a booster and cap in situ in a relatively large main explosive charge.

(FIG. 5 illustrates a step in securing a c nventional cap to the booster.

FIG. 6 and FIG. 7 are transverse sectional views showing successive steps in fastening the cap and the booster together.

FIG. 8 is a top plan view of a modified form of booster.

DESCRIPTION OF PREFERRED EMBODIMENT The booster of the present invention is formed as an approximately wedge-shaped block 11, FIG. 1. Its thinner or wedge edge 12 which is rounded is recessed or cut out for a little more than half its length to provide a semicylindrical pocket 13. The latter is shaped and sized to seat rather snugly a standard blasting cap or primer 15, FIG. 4. The arrangement is such that the center of detonation 17 of the cap or detonator is approximately at the middle of the thin rounded edge and therefore is approximately directly above the center of gravity of the booster block 11. It will be understood that the center 17 is approximately at the center of the sensitive primary explosive material 19, FIGS. 6, 7, which is located at and near the bottom, i.e., at the right end, FIGS. 4 and 5, of the primer 15. It will be understood that the detonator or initiator may be a piece of detonating fuse, although caps of conventional type are preferred.

The reason for this particular booster shape or arrangement is based on the characteristics of the detonation wave. As explained in detail in the reference mentioned above, The Science of High Expl sives, by Cook, Chapter 5, pp. 91-122, the detonation wave from the initiator, which may be considered for present purposes to be approximately the center of gravity of the sensitive primary explosive mass 19 in primer 15, develops in a conical pattern from approximately point 17 with a spherical front. Starting from center point 17, FIGS. 2 and 4, a spherical wave front indicated by curved dotted lines 20, 211, FIGS. 4 and 8, is developed as the detonation wave proceeds outward. The mass of explosive in the booster is arranged to feed this wave front to a near optimum extent as the wave front advances through the booster, thus maximizing the booster effect. The shape and proportions of the booster 11 are such that the distances from center 17 to the base 22 and the ends 23, 24 of the .booster are approximately or roughly equal. A more ideal form apparently would be segment-spherical which the booster 11 approximates as closely as is practicable. Such would closely resemble in shape a segment or two of an orange, or a thick wedge slice cut from an apple with the center of detonation at the spherical center of the apple. Such a shape is more difficult to mold; hence the design shown is a practical and convenient approximation to it. The ends 23, 24 of booster 11 may be rounded, if desired, to improve the approximation; such a form 111 is shown in FIG. 8, where rounded ends 123 and 124 are seen, the rounded edge 112 and the primer receiving recess 113 being similar to elements 12, 13 of FIG. 1.

The booster 11 may be manufactured very simply by use of a mold such as that shown at 30 in FIG. 3. This consists of a tapered wall forming mold having slightly flaring end walls 31, 32 and side walls 33 which form a trough, only one of which walls is seen in FIG. 3. The bottom of the mold is rounded at 34 to shape the rounded thin edge portion 12, FIG. 1. A cylindrical filler portion 35 fills and occupies slightly more than half the length of the bottom 34 so as to form the recess 13 when molding takes place. The flared end and side walls permit easy removal of the booster after it solidifies.

The booster is formed preferably by melting a stable castable explosive, such as pentolite or cyclotol. Any sensitive high explosive that can be liquified or rendered sufficiently fluid or plastic for molding, without decomposition, may be formed in the desired shape by either pouring or pressing it into the mold and allowing it to solidify. Because of the tapered Wedge shape of the mold and the fact that its upper edges (as shown in FIG. 3) all lie in a horizontal plane, it can be poured full and/0r leveled off to produce in sequence precisely similar pressed or molded blocks 11. The operation is simple and can be performed rapidly, either by automatic equipment or manually. Sensitive explosive such as Tetryl, resin bonded PE'FN, PETN-TNT mixtures (Pentolite), tetrytol, and combinations of any two or more of these may be used.

A combination of ingredients may be used instead of single booster compositions, if desired. Thus granules or other particles of explosive material may be placed in the mold first and bonded together by a castable explosive composition, as described in US. Patent No. 3,371,- 606, mentioned above. Materials or mixtures that can be pressed or molded, rather than cast, can be used although it is generally preferable, because it is more convenient, to cast the booster when the explosive used in it is castable.

For a given mass of booster explosive, the boosters of this invention appear to be considerably more effective than a perforate or annular booster surrounding a primer. The reason for this appears to be that a larger mass of explosive, extending radially farther from the center of detonation, is much more effective.

As mentioned above, efiicient use of boosters commonly makes it desirable to attach the primer securely to the booster. It is also desirable in many cases to be able to remove the booster from a charge. Where plans are changed, or related operations are interrupted, it is desirable to be able to remove both the primer and the booster from the charge so as not to leave any sensitive or easily detonable material in place.

A simple and highly effective method for securing the primer to the booster is shown in FIGS. 5, 6 and 7. With the primer 15 in place in its recess or seat 13, a strip of strongly adhesive tape 41 is wrapped in one, two or three convolutions around booster and primer. A plastic adhesive tape of a type commonly used for securing insulation around pipes, ducts and other conduits for heat insulation purposes, is particularly suitable, a though others may be used. When so applied, the convolutions at first may not adhere to the block 11 or to primer 15, or even to each other, as may be desired. By crimping the wrapped tape with the fingers, pressing it firmly into intimate contact at corners, crevices, and/ or by twisting. the bond becomes very secure. In an actual test, the taped primer-booster assembly had a pulling force of 8 to 10 pounds (applied to the wire or cord 16, FIG. 4) before the parts began to separate. Since a typical booster of this invention weighs only a small fraction of an ounce, this represents an adequate and highly satisfactory method of fastening. A booster can thus be pulled out of a considerable depth of explosive slurry, or of prills and oil (AN-FO) without coming loose.

The design of the booster makes it adaptable for use in slender boreholes, such as those designed for single sticks of dynamite, as represented by circle 60 in FIG. 2. The boosters of this invention are sufiiciently powerful, however, that they can be used in small or large masses of very insensitive explosives. An example of use in a larger mass 70 of aqueous blasting slurry is shown in FIG. 4.

It will be understood that various changes and modifications may be made, in addition to those described above, without departing from the spirit and purpose of the invention.

What is claimed is:

1. A booster for detonating cap-insensitive explosive charges which comprises a small wedge-shaped body of cap sensitive high explosive having a thin edge portion, a wider base opposite said portion, a primer receiving recess along only a part of said thin edge, and stop means 5 in said recess for positioning a primer cap with its center of detonation substantially opposite the center of mass of said wedge-shaped body.

2. A booster according to claim 1 which comprises a cast fusible high explosive mass selected from the group which consists of resin bonded PETN, PETN-TNT mixtures, Tetrytol and mixtures of at least two thereof.

3. A booster according to claim 2 which contains discrete explosive particles of detonation-promoting material bonded together by said cast high explosive.

4. The method of detonating a highly insensitive explosive charge which comprises fitting a primer along a thin edge of a general wedge-shaped booster in appropriate positional relationship to give an enhanced directional boostering effect to the initial detonation wave, placing said booster and primer in position with respect to said charge to amplify the boostering action, securing the primer to the booster by a wrapping which extends around the main axis of both said primer and said booster, and initiating said primer.

I References Cited UNITED STATES PATENTS 1,450,666 4/ 1923 Decker 102-24 2,629,325 2/ 1953 Sweetrnan 102-24 X 2,698,575 1/ 1955 Poulter 102-24 2,763,210 9/1956 Church et a1. 102-24 3,090,306 5/1963 Reuther 102-22 3,242,863 3/ 1966 Gipson 102-22 3,280,743 10/ 1966 Reuther 102-24 3,354,827 11/1967 Nelson 102-24 3,371,606 3/1968 Cook et a1. 102-24 3,377,953 4/ 1968 Thomanek 102-27 X VERLIN R. PENDEGRASS, Primary Examiner 

